This invention is concerned with a disc brake system, for example for a wheel of a vehicle.
A conventional disc brake system comprises a hub mounted on a suspension link for rotation relative thereto, the hub providing a mounting for a wheel, and a disc brake comprising a brake disc mounted for rotation with the hub, friction material pads arranged on opposite sides of the disc, and at least one piston and cylinder assembly operable to urge the pads into engagement with the disc, to brake the hub and hence the wheel. Conventionally, the piston and cylinder assembly is slidably mounted on a slide bolted to the suspension link of the vehicle. The disc is conventionally rigidly fixed to the hub, and wear of the pads and/or the disc is accommodated by the sliding movement of the cylinder.
Disc brake systems are known in which two discs are mounted on the same hub and rotate with the hub as a unit. Both discs can perform sliding movement on the hub, further friction material pads being provided between the discs, for example see GB 1 396 503. However, such systems are associated with technical problems. For example, since the discs are relatively thin, they tend to tilt on the hub and affect the braking ability. Also, there is a tendency for noise to be produced by rattle of the discs against the hub. At higher disc temperatures, these problems can be particularly severe since, when there is a large temperature differential, such as 600xc2x0 C., between the braking surface of a disc and the hub, the disc expands considerably, away from the hub, exacerbating the problems of tilting and rattle. These problems are addressed in WO 98/26192 in which the solution proposed is to provide a plurality of resilient force applicators which are mounted between the hub and the discs, the force applicators acting to apply radially-directed forces to the discs to control the movement thereof, the force applicators being distributed circumferentially around the hub. In one of the embodiments proposed in WO 98/26192, the force applicators are flat steel leaf springs each of which acts between the hub and both discs. This arrangement has the disadvantage that the same springs act on both discs and the action of the springs on one of the discs affects their action on the other disc. This is undesirable since the individual discs may require an individual force regime. It would be possible to provide narrower springs so that each disc could have its own individual set of springs independently mounted on the hub but this would cause assembly problems which would increase if the system had more than two discs.
It is an object of the present invention to overcome the disadvantage mentioned above without increasing assembly problems.
The invention provides a disc brake system comprising at least two discs, and a hub which is arranged to rotate about an axis thereof, the system also comprising mounting means by which the discs are mounted on the hub so that the hub and the discs rotate as a unit about said axis and the discs can perform axial sliding movement on said hub, the system also comprising a plurality of leaf springs mounted on the hub and engaging the discs so that the springs apply radial force between the discs and the hub, characterised in that the leaf springs are arranged in groups, one spring in each group acting on each disc, at least one spring in each group being retained in position by a connection to another spring in said group.
In a disc brake system according to the invention, each disc has its own individual set of springs (one from each group) and the connections between the springs can readily be arranged such that the springs operate independently of one another. Each group of springs can be assembled on the hub by securing one of the group thereto or by securing the group as a whole thereto.
A disc brake system according to the invention may be of the type disclosed in WO 98/25804. That brake system comprises two discs which are slidable on the same hub under the control of leaf springs which act between the hub and the discs. The system also comprises a cylinder which is integrally formed with a suspension link and a caliper also fixed to the suspension link, the caliper having supports for friction material pads mounted thereon. In a system according to the invention, the leaf springs which act between the hub and the discs disclosed in WO 98/25804 would be replaced by groups of springs as disclosed herein. Each spring in the group may be a flat spring similar to those disclosed in WO 98/25804 or may have one of the forms disclosed hereinafter.
Preferably, each of the springs comprises at least three abutments which project transversely of the spring and engage the disc so that the abutments apply force to the disc. Said abutments may be provided by embossed portions of the spring. Such embossments may have a generally semi-cylindrical form. Alternatively, the abutments may be provided by material deposited on the spring and secured thereto.
Said abutments may be elongated so that each abutment remains in engagement with the disc throughout said movement of the disc on the hub.
Said abutments may be in the form of ridges extending parallel to the axis about which the hub rotates.
The leaf springs of a disc brake system according to the invention may be secured to the outer surface of the hub in a manner such that the springs extend tangentially of the hub when the disc is not mounted on the hub but are resiliently deformed by mounting a disc on the hub.
In a disc brake system according to the invention, cut-outs may be formed in the leaf springs to control the force applied by the springs to the discs. Such cut-outs may be in the form of holes through the spring or may be cut into the edges of the spring.
Said mounting means of the discs on the hub may comprise axially-extending grooves formed in an external surface of said hub and teeth projecting from said discs into said grooves, the teeth being a sliding fit in said grooves. In this case, said leaf springs may be located within said grooves and engage said teeth.